1. Field of the Invention
The invention relates to a housing for electronic switchgear, in particular a housing for a proximity switch or the like.
2. The Prior Art
Electronic switchgear is known in many forms, in particular in the form of inductive, capacitive and optoelectronic proximity switches. With the aid of the metal sleeve provided with a male thread, the housing of such switchgear can be threaded into dimensionally defined threaded sockets at the site where it is to be used. The inside diameter available for accommodating the circuitry is determined by the fixedly defined outside diameter and by the wall thickness of the inner and outer sleeves. With a small outside diameter, e.g. 18 mm or less, a very small wall thickness must be provided for the inner sleeve, that is, a wall thickness of less than 0.5 mm. and preferably of approximately 0.4 mm. This requirement, however, conflicts with increasingly stringent requirements for tightness and dielectric strength of such housing. Up to now meeting these requirements generally requires potting the circuitry with insulating resin.
A particular problem arises if an optical switching state indicator that is intended to be visible from outside the outer sleeve is provided for on the circuitry positioned inside the inner sleeve. With this need in view, many attempts have been made to meet standard requirements for tightness and dielectric strength see West German Patent 30 29 595 and the prior art discussed therein. Among these known attempts at solving the problem, those that have at least made sense in principle nevertheless have proved impossible to reduce to practice, given the slight wall thickness needed.
With a wall thickness of no more than 0.5 mm. as explained above, the prior art housing with a one-piece, injection-molded inner sleeve has a maximum length of about 40 mm. For technical reasons associated with the injection molding process a greater length is impossible to obtain.